The embodiments herein relate generally to subterranean formation operations and, more particularly, to determining the depth location of loss zones in a subterranean formation.
Hydrocarbon producing wells are typically formed by drilling a wellbore into a subterranean formation. A drilling fluid is circulated through a drill bit within the wellbore as the wellbore is being drilled. The drilling fluid is produced back to the surface of the wellbore with drilling cuttings for removal from the wellbore. The drilling fluid maintains a specific, balanced hydrostatic pressure within the wellbore, permitting all or most of the drilling fluid to be produced back to the surface. However, the hydrostatic pressure of the drilling fluid may be compromised if the drill bit encounters certain unfavorable subterranean zones, such as low pressure zones caused by natural fissures, fractures, vugs, or caverns, for example, into which the drilling fluid may become lost into the formation, termed “fluid loss zones” or “loss zones.”
After a wellbore is drilled, a cement column may be placed around a casing (or liner string) in the wellbore. In some instances, the cement column is formed by pumping a cement slurry through the bottom of the casing and out through an annulus between the outer casing wall and the formation face of the wellbore. The cement slurry then cures in the annular space, thereby forming a sheath of hardened cement that, inter alia, supports and positions the casing in the wellbore and bonds the exterior surface of the casing to the subterranean formation. This process is referred to as “primary cementing.” Among other things, the cement column may keep fresh water zones from becoming contaminated with produced fluids from within the wellbore, prevent unstable formations from caving in, and form a solid barrier to prevent fluid loss from the wellbore into the formation and the contamination of production zones with wellbore fluids. However, like drilling fluid, the cement slurry may be lost to loss zones, thereby compromising the integrity of the cement column.
Stimulation of subterranean formations may be performed using hydraulic fracturing treatments. In hydraulic fracturing treatments, a treatment fluid is pumped into a portion of a subterranean formation at a rate and pressure such that the subterranean formation breaks down and one or more fractures are formed. Typically, particulate solids are then deposited in the fractures. These particulate solids, or “proppant particulates” or “proppant,” serve to prevent the fractures from fully closing once the hydraulic pressure is removed by forming a proppant pack. As used herein, the term “proppant pack” refers to a collection of proppant particulates in a fracture. By keeping the fracture from fully closing, the proppant particulates aid in forming conductive paths through which fluids may flow. During stimulation, the fracturing fluid may become lost to loss zones, as well. In such circumstances, the fracturing operation may be compromised, the proppant particulates may no longer be adequately suspended for placement into a fracture, and the like.
The consequences of fluid loss can be economically and environmentally devastating, ranging from minor volume loss of treatment fluids (e.g., drilling fluids, cement slurries, fracturing fluids, and the like), to delayed drilling and production operations, to an underground well blow-out, and the like. Therefore, the occurrence of fluid loss during hydrocarbon well operations typically requires immediate remedial steps. Remediation often involves introducing a composition into the wellbore to seal unfavorable subterranean zones and prevent leakoff of the treatment fluids within the formation to loss zones. Such compositions are generally referred to as “loss circulation materials.”
However, treating a loss zone may be ineffective because the exact location of the zone is unknown. Moreover, because the loss zone location is unknown, the amount of loss circulation materials must often be sufficient to cover the entire length of a wellbore, even though only a small percentage of the wellbore may require treatment, thereby leading to inefficient materials use and associated costs.